1. Field of the Invention
The present invention relates to a non-contact portable data storage device, generally referred to as a non-contact IC card, which exchanges signals with an external apparatus by using electromagnetic waves or light and, more specifically, to a structure for increasing the mechanical strength of such a storage device.
2. Description of the Related Art
In recent years, non-contact portable storage devices (hereinafter referred to as "non-contact IC cards") which exchange signals with external apparatus by means of electromagnetic waves have been used in various fields. A non-contact IC card includes a circuit board on which circuitry comprising a semiconductor integrated circuit and the like, and an antenna circuit for exchanging signals with an external apparatus are mounted, and which is encased in a card-shaped card body.
FIG. 7 schematically shows, in a block diagram, the functional arrangement of a non-contact IC card of the above-described kind. The card includes a CPU 1 for data processing and control within the non-contact IC card, the CPU 1 being connected via a bus 8 with a ROM 2 and a RAM 3 together being part of a data storage section, and an input/output control circuit 4. The input/output control circuit 4 controls data to be input to or output from the card, and is connected with an antenna circuit 6 through a modulating-demodulating (MODEM) circuit 5. A battery 7 is provided to supply power to the above-described components. The antenna circuit 6 exchanges signals with an external apparatus (not shown) by means of electromagnetic waves 6a.
FIG. 8 is a perspective plan view for explaining an actual internal structure of a conventional non-contact IC card. FIG. 9 is a sectional view of the card, taken along line IX--IX shown in FIG. 8. In FIG. 8, the card is shown in a state where a molding resin 13 sealing a circuit board 11 and various components thereon is removed. Referring to these figures, a non-contact IC card 10 includes a circuit board 11, and, in the center of the circuit board 11, an IC 9, other circuit elements 9a, a battery 7, mounted in such a manner as to be connected with each other by a circuit pattern 11a on the circuit board 11. The circuit elements 9a comprise a capacitor, an inductance, a resistor and the like. Elements corresponding to those denoted by reference numerals 1 through 5 and reference numeral 8 in FIG. 7 are provided within the IC 9.
The non-contact IC card 10 also includes an antenna circuit 6 comprising a spiral coil 61 provided on the outer peripheral portion of the circuit board 11, and a capacitor 63. The spiral coil 61 and the capacitor 63 are connected in parallel as an LC parallel resonance circuit across which a voltage induced in the circuit by electromagnetic waves in the vicinity of the resonance frequency appears. The spiral coil 61 comprises a pair of spiral-shaped conductor patterns 61a and 61b respectively on first and second major surfaces of the circuit board 11. The conductor pattern 61a and 61b respectively on point A (shown in FIG. 8) on the first major surface, or the front surface, of the circuit board 11, and is connected, by passing through a through-hole 12a, to the other conductor pattern 61b on the second major surface, or the back surface, of the circuit board 11. The back-surface conductor pattern 61b extends in a spiral shape from the through-hole 12a to an inward location, and has an inner end passed through another through hole 12b and connected to, for instance, the ground side, of the battery 7 on the front surface.
The spiral coil 61 has an inductance L, and is connected in parallel with the capacitor 63 having a capacitance C. The circuit board 11 having the above-described construction is encapsulated in a molding resin 13, comprising a resin such as a non-electrically-conductive resin, for forming a card body, so as to minimize external influence on the transmission of electromagnetic fields. Another example of the card body is a hollow casing comprising, for instance, a frame body and a pair of panels.
A conventional non-contact portable storage device (non-contact IC card) having the above-described construction has the following problem. When the card has a relatively large thickness, it is possible to assure the necessary mechanical strength with respect to bending or twisting only by adopting a suitable resin composition. However, when the thickness of the card is to be reduced (for instance, to a thickness of the order of 1 mm), it becomes difficult to assure the necessary mechanical strength only by adjusting the resin composition. A method which may be adopted to assure the necessary mechanical strength comprises providing an electrically-conductive metal cover. However, such a cover can, as a matter of course, have a great influence on the transmission of electromagnetic fields, and the method is not practical.